[FIX] web: stop defaulting on empty kanbans when you should not

1/ Write a form view with a o2m field that has its own inline tree view
(no other view exist in db for the target model)
2/ Open that view in a mobile environment
3/ Instead of having a list view, you get a kanban view. No luck for
you, since the default kanban generated by `models.py` is an empty one,
your records are *invisible* \o/

From what I can tell, the previous condition made no sense:
```
if (there is a list view and a kanban view)  <-- this seems absurd
  then (use the list mode)
elif (there is no list view but a kanban view)
 then (use the kanban mode)
else (use both modes)
```

The first condition seems absurd: it *actively* ignores a kanban view
if there is one. Even better, the list view whose existence it checks
is never there: it checks for a `tree` when it should be checking for a
`list`. In short, the first condition was *never* met, and you ended up
either with exclusive kanban mode or with both modes - even if you had
no existing kanban view for the target model...

This commit moves the normalization of `tree` into `list` before
attempting to process the x2many field's subviews. It clarify the usage
of `tree` vs `list` (cf. only use `list`) which  prevents weird edge
cases like described above.

closes odoo/odoo#36237

Signed-off-by: Adrien Dieudonné (adr) <adr@odoo.com>
Co-authored-by: Adrien Dieudonné <adr@odoo.com>
Co-authored-by: Pierre Paridans <app@odoo.com>

1 files changed, 13 insertions, 14 deletions

diff --git a/addons/web/static/src/js/views/basic/basic_view.js b/addons/web/static/src/js/views/basic/basic_view.js
index 38d2f220c2f..5cb293e866b 100644
--- a/addons/web/static/src/js/views/basic/basic_view.js
+++ b/addons/web/static/src/js/views/basic/basic_view.js
@@ -282,29 +282,28 @@ var BasicView = AbstractView.extend({
             });
         }
 
+        attrs.views = attrs.views || {};
+
+        // Keep compatibility with 'tree' syntax
+        attrs.mode = attrs.mode === 'tree' ? 'list' : attrs.mode;
+        if (!attrs.views.list && attrs.views.tree) {
+            attrs.views.list = attrs.views.tree;
+        }
+
         if (field.type === 'one2many' || field.type === 'many2many') {
             if (attrs.Widget.prototype.useSubview) {
-                if (!attrs.views) {
-                    attrs.views = {};
-                }
                 var mode = attrs.mode;
                 if (!mode) {
-                    if (attrs.views.tree && attrs.views.kanban) {
-                        mode = 'tree';
-                    } else if (!attrs.views.tree && attrs.views.kanban) {
+                    if (attrs.views.list && !attrs.views.kanban) {
+                        mode = 'list';
+                    } else if (!attrs.views.list && attrs.views.kanban) {
                         mode = 'kanban';
                     } else {
-                        mode = 'tree,kanban';
+                        mode = 'list,kanban';
                     }
                 }
                 if (mode.indexOf(',') !== -1) {
-                    mode = config.device.isMobile ? 'kanban' : 'tree';
-                }
-                if (mode === 'tree') {
-                    mode = 'list';
-                    if (!attrs.views.list && attrs.views.tree) {
-                        attrs.views.list = attrs.views.tree;
-                    }
+                    mode = config.device.isMobile ? 'kanban' : 'list';
                 }
                 attrs.mode = mode;
                 if (mode in attrs.views) {